package com.smart.util;

import java.nio.charset.Charset;

/**
 * BASE58工具类
 * 
 * @Author Sunxin
 */
public final class Base58 {

	private static final char[] ALPHABET = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz".toCharArray();

	private static final int[] INDEXES = new int[128];

	private static final Charset CHARSET = Charset.forName("UTF-8");

	static {
		for (int i = 0; i < INDEXES.length; i++) {
			INDEXES[i] = -1;
		}
		for (int i = 0; i < ALPHABET.length; i++) {
			INDEXES[ALPHABET[i]] = i;
		}
	}

	public static String encodeString(String input) {
		if (input == null) {
			return null;
		}

		return encodeString(input.getBytes(CHARSET));
	}

	public static String encodeString(byte[] input) {
		if (input == null) {
			return null;
		}

		return new String(encode(input), CHARSET);
	}

	public static byte[] encode(String input) {
		if (input == null) {
			return null;
		}

		return encode(input.getBytes(CHARSET));
	}

	public static byte[] encode(byte[] input) {
		if (input == null || input.length == 0) {
			return input;
		}

		// Encodes the given bytes in base58. No checksum is appended.

		input = copyOfRange(input, 0, input.length);
		// Count leading zeroes.
		int zeroCount = 0;
		while (zeroCount < input.length && input[zeroCount] == 0) {
			++zeroCount;
		}
		// The actual encoding.
		byte[] temp = new byte[input.length * 2];
		int j = temp.length;

		int startAt = zeroCount;
		while (startAt < input.length) {
			byte mod = divmod58(input, startAt);
			if (input[startAt] == 0) {
				++startAt;
			}
			temp[--j] = (byte) ALPHABET[mod];
		}

		// Strip extra '1' if there are some after decoding.
		while (j < temp.length && temp[j] == ALPHABET[0]) {
			++j;
		}
		// Add as many leading '1' as there were leading zeros.
		while (--zeroCount >= 0) {
			temp[--j] = (byte) ALPHABET[0];
		}

		return copyOfRange(temp, j, temp.length);
	}

	public static byte[] decode(byte[] input) {
		if (input == null) {
			return input;
		}

		return decode(new String(input, CHARSET));
	}

	public static byte[] decode(String input) {
		if (input == null) {
			return null;

		} else if (input.length() == 0) {
			return new byte[0];
		}

		byte[] input58 = new byte[input.length()];
		// Transform the String to a base58 byte sequence
		for (int i = 0; i < input.length(); ++i) {
			char c = input.charAt(i);

			int digit58 = -1;
			if (c >= 0 && c < 128) {
				digit58 = INDEXES[c];
			}
			if (digit58 < 0) {
				throw new IllegalArgumentException("Illegal character " + c + " at " + i);
			}

			input58[i] = (byte) digit58;
		}
		// Count leading zeroes
		int zeroCount = 0;
		while (zeroCount < input58.length && input58[zeroCount] == 0) {
			++zeroCount;
		}
		// The encoding
		byte[] temp = new byte[input.length()];
		int j = temp.length;

		int startAt = zeroCount;
		while (startAt < input58.length) {
			byte mod = divmod256(input58, startAt);
			if (input58[startAt] == 0) {
				++startAt;
			}

			temp[--j] = mod;
		}
		// Do no add extra leading zeroes, move j to first non null byte.
		while (j < temp.length && temp[j] == 0) {
			++j;
		}

		return copyOfRange(temp, j - zeroCount, temp.length);
	}

	// number -> number / 58, returns number % 58
	private static byte divmod58(byte[] number, int startAt) {
		int remainder = 0;
		for (int i = startAt; i < number.length; i++) {
			int digit256 = (int) number[i] & 0xFF;
			int temp = remainder * 256 + digit256;

			number[i] = (byte) (temp / 58);

			remainder = temp % 58;
		}

		return (byte) remainder;
	}

	// number -> number / 256, returns number % 256
	private static byte divmod256(byte[] number58, int startAt) {
		int remainder = 0;
		for (int i = startAt; i < number58.length; i++) {
			int digit58 = (int) number58[i] & 0xFF;
			int temp = remainder * 58 + digit58;

			number58[i] = (byte) (temp / 256);

			remainder = temp % 256;
		}

		return (byte) remainder;
	}

	private static byte[] copyOfRange(byte[] source, int from, int to) {
		byte[] range = new byte[to - from];
		System.arraycopy(source, from, range, 0, range.length);

		return range;
	}
	
	private Base58() {
	}
}
